In the field of making cardboard, heavy paper, or paperboard, recycled newsprint (ONP), old magazine grades (OMG), coated broke and old corrugated containers (OCC) are often used as ingredients. Contaminants such as waxes, hot melts, pressure sensitive adhesives, latex, or binder materials are usually present in these types of materials in varying quantities. Waxes, hot melts and pressure sensitive adhesives are generally referred to as stickies because they become separated from the pulp and stick to the paper making equipment and accessories. The stickies, if not treated or removed, can cause problems with running paper machines and paper quality defects.
In addition to the stickies, pulp suspensions also have colloidal anions, such as wood resins and fatty acids, referred to as anionic trash. Anionic trash needs to be controlled, otherwise, the trash will contribute to the deposit problems and will interfere with fiber-to-fiber bonding. The more problematic of the anionic trash is the wood resins and fatty acids since they form pitch or tacky deposits on the paper machine and related equipment, if not treated.
Many different substances are currently used for pitch and stickies control. Such substances include, but are not limited to chemicals (coagulants, polyamine, polydadmacs, polyethyleneimines, surfactants), talc, bentonite, precipitated calcium carbonate, and diatomaceous earth. Chemicals are only partially effective in controlling pitch and, in addition, are expensive additives. While chemicals are partially effective in controlling pitch, chemicals are generally ineffective in stickies control.
If stickies are not controlled, the paper machine must be shut down periodically to remove the stickies and render the equipment usable. Methods such as pressing, fabric wash-ups, and boil-outs are usually practiced to remove stickies. As one can imagine, shutting down the paper machine to remove stickies is an expensive and time consuming undertaking.
Pigments such as talc, bentonite, PCC and diatomaceous earth are also being used for their adsorptive properties. PCC can only be used in a neutral or alkaline pH environment since PCC dissolves in an acid pH environment to form lime and carbon dioxide. Diatomaceous earth, while able to be used in any pH environment, is very abrasive and has a tendency to adhere to parts of the paper making equipment. The use of diatomaceous earth requires the replacement and/or cleaning of various pieces of equipment more often than other types of adsorptive materials. Bentonite, like talc, can be used in any pH environment. However, unlike talc, the bentonite is less effective in controlling adhesives, waxes and hot melts.
Talc is naturally hydrophobic. Talc, in its natural state, has anionic sites at the edges of each particle. This anionicity makes talc (in its natural form) less effective than chemical polymers in dealing with pulp slurries with high levels of anionic trash since the anionic sites on the talc will repel the anionic trash present in the slurry or furnish. The treatment of talc with chemical polymers, specifically polydadmacs, has been described in at least U.S. Pat. No. 4,964,955 and U.S. patent application Ser. No. 60/327,638 filed on Oct. 5, 2001. While the polydadmac treated talc has been effective in some paper making applications, this form of cationic treatment does not appear to be as effective in controlling stickies in pulp slurries that contain high levels of waxes, hot melts and pressure sensitive adhesives.
Fillers such as talc, bentonite, and diatomaceous earth also impact other properties of the paper or board, especially when excessive amounts of the fillers are added to the pulp furnish. For instance, fillers can affect the strength of the board by negatively impacting fiber-to-fiber bonding. Fillers also reduce stiffness and can affect the coefficient of friction of the boards. A minimum value of a coefficient of friction is needed; otherwise, boards stacked on top of each other will not stack but will slide off the board located below it. This makes the boards hard to store and transport.
Thus, an additive, which can be added in amounts that do not affect other properties of the paper or boards, is needed which will effectively control stickies formation and remove anionic trash.